The number of opportunities for the use of inkjet recording methods have recently increased in fields such as the production of large-sized, outdoor advertisements requiring a large image surface area.
Durable polyvinyl chloride-based sheets able to withstand outdoor use are used as base materials used in these applications in the manner of sheets composed of vinyl chloride resin per se as well as tarpaulin sheets made of composite materials. Photocurable ink compositions for inkjet printing that do not use volatile components have been proposed for use as inkjet printing ink used for printing on such polyvinyl chloride-based sheets.
However, ink compositions must be able to form a tough coating to enable the above-mentioned outdoor advertisements and the like to withstand wind and rain. However, ink compositions capable of forming a tough film with a photocurable material typically tend to have high coating hardness and decreased adhesion to the base material. Therefore, in order to improve the adhesion to a base material of such ink compositions, methods have been employed in which a component that dissolves the base material is contained in a portion of the ink. For example, an active energy beam-curable inkjet ink for use with polyvinyl chloride-based sheets has been proposed that contains an ethylenic double bond-containing compound that does not dissolve polyvinyl chloride and an ethylenic double bond-containing compound (N-vinylcaprolactam) that dissolves polyvinyl chloride at a specific ratio (see, for example, Patent Document 1).
However, in the case of producing a printed article using this type of inkjet ink, although adhesion to a polyvinyl chloride-based sheet is favorable, there is the problem of increased susceptibility to the occurrence of cockling (phenomenon in which the base material becomes wrinkled).
In addition, in the case of curing an image using a high-energy light source commonly used in the past such as a metal halide lamp, there are problems such as the generation of ozone, increased size of the radiation device and a short lamp life. Consequently, low-energy light-emitting diode lamps (LED lamps) have come to be used for the light source in recent years. Therefore, there is a need for correspondingly enhanced levels of curability and printing performance (such as improved adhesion and cockling).
Moreover, there has also recently been a strong desire for safer photocurable ink compositions for inkjet printing that correspond to Category 4 flammable liquids (liquids having a flash point of higher than 60° C. and equal to or lower than 93° C.) as defined in GHS (Globally Harmonized System of Classification and Labeling of Chemicals) based on concerns regarding safety and health.
In addition, there is also a demand for these photocurable inks for inkjet printing to be used in outdoor seal applications in addition to outdoor advertising, thereby requiring photocurable inks for inkjet printing to have stretchability of the cured film obtained by the curing thereof.